This is on the back of previous posts. Firstly, not all Christians believe same sex relationships are wrong. But let’s say for arguments sake that it is wrong. This doesn’t mean it should not be legalised. If we take the viewpoint I have talked about in previous posts, it should absolutely be legalised. Jesus asked people to follow him and follow his guidelines for life. But if they chose to walk away and not follow him, he let them. He didn’t chase after them and demand they abide by his rules, he just let them leave and choose their own lifestyles. If non-Christians are choosing same sex relationships, who are Christians to come along and tell them they are living in sin according to their rules, which the people they are yelling at did not sign up for?

Exactly, "Who are Christians to come along and tell them they are living in sin?"Who are they? What gives Christians the right to tell people about how they should live? I think that this is an excellent question. It very much cuts to the heart of what a Christian's role is in the world, which I believe to be several.
Specifically I think that this question brings to light the Christian's role as Christ's Ambassadors. Paul sums this up nicely in his 2nd Letter to the Corinthians:

Now then, we are ambassadors for Christ, as though God were pleading through us: we implore you on Christ’s behalf, be reconciled to God.

- 2 Corinthians 5:20 (NKJV)

What then is an Ambassador? An Ambassador is the highest ranking diplomat, sent to a foreign nation bearing the representation and protection of the interests and nationals of the sending state.
It must be said that an Ambassador of themselves has no authority other than what has been conferred on them by the nation which sent them; because they speak on behalf of their nation, they act with the interests of their nation and ruler as their prime directive.

Not only are Ambassadors charged with speaking up for the nation which they represent, if they do not do so then this amounts to a dereliction of duty. An Ambassadors who does not speak up for the nation which they represent has utterly failed in their appointment and it would be best if they were fired from the role.
To this end, Ambassadors very much speak out against things which their nation finds repulsive and abhorrant. National Ambassadors regularly speak out against corruption, human rights abuses, and against belligerent powers who seek to destroy other nations and perhaps even their own people. Ambassadors also speak up for their nation on matters such as trade, treaties and cooperative agreements.

Australia for intance has Ambassadors to powers that we find unfriendly such as Laos and Libya, to powers that we are on speaking terms with but still are cautious with like China, to powers that we are very friendly with like the United States, New Zealand and the UK and to supra-national powers like the EU, NATO and the UN.
If our Ambassadors failed to speak up against human rights abuses in China, against the horror taking place in Libya and the corruption in Laos, we'd fire the Ambassadors.

This is on the back of previous posts. Firstly, not all Christians believe same sex relationships are wrong. But let’s say for arguments sake that it is wrong. This doesn’t mean it should not be legalised. If we take the viewpoint I have talked about in previous posts, it should absolutely be legalised.

Firstly, it does not matter what Christians believe. It matters entirely what God thinks. An Ambassador who believes something which falls outside of the purview of the one who sent them, has no authority to speak on such matters. Besides which, God has made it pretty clear what he thinks:

"For this reason God gave them up to vile passions. For even their women exchanged the natural use for what is against nature. Likewise also the men, leaving the natural use of the woman, burned in their lust for one another, men with men committing what is shameful, and receiving in themselves the penalty of their error which was due."

—Romans 1:26-27 (NKJV)

"Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God."

— 1 Corinthians 6:9-10 (NKJV)

"Knowing this: that the law is not made for a righteous person, but for the lawless and insubordinate, for the ungodly and for sinners, for the unholy and profane, for murderers of fathers and murderers of mothers, for manslayers, for fornicators, for sodomites, for kidnappers, for liars, for perjurers, and if there is any other thing that is contrary to sound doctrine,"

— 1 Timothy 1:9-10 (NKJV)

Legalising something has the effect of making something which was previously unlawful, lawful. Suggesting something should be legalised, exactly implies that one thinks that is is perfectly fine to perform an act.
If a Christians does happen to believe that same-sex marriages should be legalised, then they obviously condone them and need to seriously consider what they believe.

As for this remark...

Jesus asked people to follow him and follow his guidelines for life. But if they chose to walk away and not follow him, he let them. He didn’t chase after them and demand they abide by his rules, he just let them leave and choose their own lifestyles.

...I refer to the story of the woman at the well in John 8:

When Jesus had raised Himself up and saw no one but the woman, He said to her,“Woman, where are those accusers of yours? Has no one condemned you?”

She said, “No one, Lord.”

And Jesus said to her, “Neither do I condemn you; go and sin no more.”

Then Jesus spoke to them again, saying, “I am the light of the world. He who follows Me shall not walk in darkness, but have the light of life.”

- John 8:10-12 (NKJV)

Whilst it may be true that Jesus didn't condemn the woman, it certainly does not mean that he either excused her or gave her licence to continue on in her sin. In fact he directly told her "go and sin no more".
Further to this, he actually made a point that once people have decided to follow Jesus and been told where they've gone wrong, that they no longer continue to "walk in darkness, but have the light of life".

I also think that Christians do not have the right to condemn people. We are actually no better than anyone else in the world. Whilst some of us might like to adopt airs of piousness which really help no-one, the point is that the only difference between a Christian and someone else, is that the Christian admits that they are a hopeless case, can not save themselves from the sin and mess they've made and are in need of a saviour. If for only that reason alone, then we should be acting as Ambassadors and speak as someone with no authority except that which has been charged to us.

To summarise:

Who are Christians to come along and tell them they are living in sin?

They are Christ's Ambassadors, charged with the job of speaking out and speaking up on behalf of God and his purposes; to fail to do so is a dereliction of duty. This general principle not only counts for just the case of same-sex marriage, but EVERYTHING.

Devils Advocate interjects - Was very well said sir, but if another Christian holds a different perspective based on a Biblical understanding do they have just as much right to speak up, would it not be as much a dereliction of duty if they did not?

Cool, what do you say to having a right to speak up based not on a biblical understanding (or did you cover this already) but on a personal understanding of God or an understanding wrought from elsewhere, from other literature for example? Does that step out of the bounds of being an ambassador for Christ?

If you are going to talk about God without a biblical understanding, then it would have to be consistent with what we already know about God. I'm not suggesting that we can't find out about what God is like, without reference to the Bible, however it's best to check what people have to say with what we already know.It's a question of standards really. Does something which someone have to say about God agree or disagree with what God himself has already told us?

Perhaps the words of Jesus himself are useful:Beware of false prophets, who come to you in sheep’s clothing, but inwardly they are ravenous wolves. You will know them by their fruits. Do men gather grapes from thornbushes or figs from thistles? Even so, every good tree bears good fruit, but a bad tree bears bad fruit. A good tree cannot bear bad fruit, nor can a bad tree bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. Therefore by their fruits you will know them.- Matthew 7:15-20

Obviously it stands to reason that if someone says something about God which doesn't add up, then it should be treated with suspicion. God gave us brains and minds to think with, we should use them to test everything, even what comes from a pulpit... in fact don't just blindly believe what I've said. Go away and test it against scripture as well!